In the seminiferous tubule, the large, round nuclei belong to more mature primary spermatocytes. Toward the lumen from these are the nuclei of spermatids.

Note the occasional Sertoli cell nuclei and try to follow the extensive Sertoli cell cytoplasm as it passes up to enfold the spermatocytes and spermatids. In the interstitial tissue, observe the Leydig cells and capillaries (the latter are somewhat swollen because the testis was fixed for electron

Reference: Michigan Histology and Virtual Microscopy Learning Resources
https://histology.medicine.umich.edu/resources/male-reproductive-system#electron-micrographs